Heterosexual transmission accounts for the fastest growing risk group of people with HIV/AIDS and is the chief mode of affection among women in the United States. Research has shown that there is a continued low rate of condom use among heterosexuals in established relationships. Young adult crack/cocaine and heroin abusing patients and their primary sexual partners rank among those at highest risk for heterosexual HIV/STI transmission. A growing body of research, including recent randomized clinical trials, has found that couple-based approaches to HIV risk reduction are efficacious in increasing condom use. The proposed study will rigorously test the efficacy of a couple-based HIV/STI prevention intervention to increase condom use and reduce sexually transmitted infections (STIs) among heroin or crack/cocaine abusing, outpatient drug treatment or methadone maintenance patients, aged 18-35, and their main heterosexual partners, who are both HIV negative and report risk of sexually-acquired HIV. This study will enroll 450 index participants, aged 18 to 35, who will be recruited from an MMTP or outpatient drug treatment program for crack/cocaine and/or heroin abuse, and their main heterosexual partners and who will report having had unprotected sex and at least one risk factor for HIV in the past 90 days. The index participants and their main heterosexual partners will be randomized to one of three conditions: a 7-session couple-based HIV/STI risk reduction intervention (CSTI) provided to the index participant and her/his main partner; a 7-session couple-based stress reduction intervention (CSR) provided to the index participant and her/his main partner, which will serve as a attention control condition; and a 7-session individual HIV/STI risk reduction intervention (ISTI) provided to the index participant alone, which will serve as a comparison condition. Dr. E1-Bassel, the Social Intervention Group (SIG) investigative team and Dr. Remien, from the HIV Center for Clinical and Behavioral Studies at the NY State Psychiatric Institute, will lead the study. In addition, several consultants will be involved in the study: Dr. Steinglass from the Ackerman Institute for the Family, Dr. Long shore from the University of California at Los Angeles, Dr. Sharp from St. Luke's Hospital in New York City, and Dr. Fals-Stewart from the Research Institute on Addictions at the University of Buffalo. [unreadable] [unreadable] [unreadable]